How to Choose Positioning Technologies for Indoor Construction Management: Comprehensive Comparison of GPS Alternative Systems

Table of Contents

• The importance of location information technologies in indoor construction management

• Why GPS cannot be used indoors and the related challenges

• Main types of indoor positioning technologies (GPS alternative systems) - Wi-Fi-based indoor positioning - Indoor positioning using Bluetooth beacons - UWB (Ultra-Wideband radio) for high-precision positioning - Position management using RFID tags and NFC - Inertial sensors and PDR (Pedestrian Dead Reckoning) - Image recognition and marker-based position estimation

• Key points when choosing indoor positioning technologies

• Recommendation for simple surveying using LRTK

• FAQ

The Importance of Location Information Technology in Indoor Construction Management

In construction site management, location information—"who," "where," and "what they are doing"—is an extremely important element. Especially on indoor construction sites, location information is closely tied to tracking workers' whereabouts, safety management, and the location management of materials and equipment. For example, in interior work on large-scale building projects, if you can grasp the real-time locations of workers on each floor or in each area, it leads to improved work efficiency and faster responses in emergencies. Also, if you can instantly confirm where construction materials are stored, you can reduce the time spent searching and prevent schedule delays. In this way, the use of location information in indoor construction management is the key to enhancing on-site safety and productivity.

However, obtaining location information in indoor environments is not easy. Outdoors, you can easily get the current position of a smartphone or a positioning device using satellite positioning systems (such as GPS), but GPS hardly works underground or inside buildings. Therefore, indoor construction management requires the introduction of alternative positioning technologies to replace GPS. This article thoroughly compares the reasons why GPS cannot be used indoors and the types of indoor positioning systems that can serve as alternatives, and explains the key points for selecting technologies that match on-site needs.

Reasons and Challenges Why GPS Can't Be Used Indoors

Familiar from car navigation systems and smartphone map apps, GPS (Global Positioning System) is also widely used in the construction industry for tasks such as locating heavy equipment and surveying. However, GNSS (Global Navigation Satellite System), including GPS, relies on radio signals from satellites, so indoors its accuracy often degrades drastically or positioning is frequently impossible. The main reasons and challenges include the following.

• Radio signals cannot reach / are shielded: Indoors and underground, building walls, ceilings, and the ground act as obstacles that prevent the weak radio signals from GPS satellites from reaching the receiver. Also, inside reinforced concrete buildings radio waves are prone to reflection and attenuation, so stable reception like outdoors cannot be achieved.

• Errors due to multipath: Even if GPS signals can be received indoors, radio waves reflecting off walls and large equipment cause multipath (multiple-path) effects, resulting in significant positioning errors. Deviations on the order of several meters to several tens of meters occur, making GPS unusable for precise management of indoor work.

• Determining vertical position: Standard GPS can determine horizontal position but has difficulty accurately identifying height (the floor). In structures with overlapping floors, such as high-rise buildings or underground levels, it is challenging to determine “which floor” someone is on using GPS alone.

For these reasons, GPS cannot be relied on for indoor construction management. Instead, it is necessary to deploy positioning technologies that can be used in indoor environments (in other words, GPS alternative systems). In the next chapter, we will introduce the representative types and characteristics of indoor positioning technologies and compare their respective advantages and disadvantages.

Main Types of Indoor Positioning Technologies (GPS Alternative Systems)

There are various technologies for obtaining and tracking location information indoors. Here, we discuss the main indoor positioning technologies expected to be useful on construction management sites, explaining how they work and their characteristics. These systems, which can serve as alternatives to GPS, vary in accuracy, cost, and ease of deployment depending on the usage environment and purpose. Understanding each technology and selecting the most suitable method for the site is important.

Indoor Positioning Using Wi‑Fi

Wi‑Fi positioning is a technology that estimates a device's location by leveraging existing Wi‑Fi access points (wireless LAN routers). By analyzing the signal strength (RSSI) and time of arrival of the radio signals received by smartphones or dedicated devices from multiple Wi‑Fi access points installed within a building, it determines an approximate current location.

• Feature: The advantage is that you can use the existing Wi‑Fi infrastructure without adding special dedicated equipment. If workers have Wi‑Fi‑capable devices such as smartphones, position data can be collected through an app. It has a low introduction cost and is a relatively easy method to try.

• Accuracy: In general, accuracy is on the order of several meters to several tens of meters (a few m (a few ft) to several tens of m (several dozen ft)), so it is not very high. It is affected by radio conditions; in offices and commercial facilities you can estimate positions with errors of a few meters (a few ft), but in buildings under construction with many walls radio reflection and attenuation tend to increase errors. It can also be difficult to distinguish different floors using Wi‑Fi signals alone.

• Benefits: Because you can reuse the existing Wi‑Fi environment, the initial cost is low, and because you can use smartphones rather than dedicated tags it is easy to introduce. There is also no burden on workers to carry additional devices.

• Drawbacks: Because positioning accuracy is coarse, it is not suitable for construction management tasks that require accuracy in the centimeter or tens-of-centimeters range (centimeters (in) or tens of cm (in)). Also, areas where Wi‑Fi signals do not reach cannot be positioned, so radio-environment setup or adjustment is required. It is also unsuitable for real-time tracking down to second-level movements.

Indoor Positioning with Bluetooth Beacons

Bluetooth beacons refer to small transmitters that use Bluetooth Low Energy (BLE). The method of receiving the weak radio signals emitted from beacons with a smartphone or receiver and estimating position from factors such as received signal strength and time-of-arrival differences is known as beacon positioning. It is used for navigation services in museums and commercial facilities, and is expected to be applied to managing the locations of workers and materials on construction sites.

• Feature: BLE beacons are inexpensive and compact, and because they are battery-powered and easy to install, they can be deployed in large numbers across wide indoor spaces. Each beacon has a simple design that only transmits a unique ID, so post-installation maintenance is relatively easy. Reception is handled by smartphones or dedicated gateways.

• Accuracy: The positioning accuracy of beacons is generally considered to be about 1–5 m (3.3–16.4 ft). This is because the distance between the beacon and receiver is estimated from signal strength, and reflections or interference from walls and equipment can introduce errors. Advanced systems may triangulate signals from multiple beacons to aim for accuracy within a few meters, but in environments with many obstacles, such as construction sites, errors tend to increase.

• Advantages: A major advantage is that costs are relatively low. Beacons themselves are inexpensive, making it easy to distribute tags to individual workers or materials. Also, because power consumption is low, many models can operate on batteries for about six months to one year, allowing installation without wiring. If integrated with a smartphone app, collecting and notifying location information is also straightforward.

• Disadvantages: A challenge is that they are susceptible to environmental influences. On construction sites with many steel frames or concrete walls, Bluetooth signals are easily obstructed or attenuated, and the expected accuracy may not be achieved. Also, covering a wide area requires many beacons, so initial setup and maintenance become more burdensome at large sites. Furthermore, when movement between floors occurs, vertical positioning is difficult and supplementary measures are necessary.

High-precision positioning using UWB (Ultra Wideband)

UWB (Ultra Wideband) is a wireless technology that uses ultra-wideband radio waves in the 3.1–10.6 GHz band and is a high-precision indoor positioning system that has attracted attention in recent years. It computes positions by combining extremely short pulse signals with techniques such as ToF (time-of-flight measurement of radio waves) and TDoA (time-difference-of-arrival measurement). By placing multiple UWB anchors (fixed stations) inside a building and rapidly measuring the distances to UWB tags attached to workers and equipment, position coordinates can be obtained in real time.

• Features: Because UWB uses nanosecond-level short pulses, it is less affected by reflections from metal and can achieve high positioning accuracy. Generally, it is possible to improve accuracy to the range of tens of centimeters down to the 10-centimeter level (10 cm (3.9 in)), making it one of the most accurate indoor positioning technologies. Practical use has begun in asset tracking at manufacturing plants and warehouses, equipment management in hospitals, and it is a strong candidate in construction management for scenes that require precise position control at the millimeter level.

• Accuracy: With an appropriate system configuration, it can achieve positioning errors of less than 1 m (3.3 ft), and in some cases on the order of 10 cm (3.9 in). It is overwhelmingly more accurate than other wireless methods (Wi-Fi or BLE) and enables real-time tracking. However, to achieve high accuracy, multiple anchors need to be installed within line-of-sight distances, and depending on the environment, measures against radio interference and optimization of antenna placement may be required.

• Benefits: The greatest benefit is its extremely high accuracy. It can be applied to tasks requiring precision, such as automated control of heavy machinery, robot guidance, and verification of structure installation positions. In addition, the positioning data update rate is high, allowing near-real-time tracking of people and objects that move dynamically.

• Drawbacks: The main drawback is the high introduction cost. UWB-compatible tags and anchors are more expensive than other methods, and covering a wide area requires a considerable upfront investment. System construction is also sophisticated and may require specialized knowledge for configuration tuning and operation. Due to the characteristics of radio waves, it is difficult to perform positioning across rooms completely separated by walls or floors, so it is necessary to build an anchor network for each floor. Depending on the placement of metal objects or machinery in the environment, careful antenna positioning may be required.

Position Management Using RFID Tags and NFC

RFID (Radio Frequency Identification) and NFC (Near Field Communication) are technologies that attach wireless tags to objects and identify where the object is by communicating with a reader device. These are used to determine that an object has "passed a specific point" or is "present in a certain area," rather than strictly measuring continuous real-time position coordinates.

• Features: RFID has passive tags that require no battery and active tags with built-in batteries. On construction sites, one conceivable use is attaching tags to tools and materials and reading them with gate-type readers to manage inbound/outbound inventory. NFC is a mechanism for reading and writing information by holding a tag and reader extremely close (on the order of a few cm (a few in)), so use cases such as workers tapping a smartphone at checkpoints to leave patrol records are also possible.

• Accuracy: The concept of positioning accuracy does not really apply, but RFID estimates location based on whether a tag is within the reader’s read range (antenna output). High-power RFID readers can detect tags several meters (several ft) away, but basically it only determines whether something is inside an area or not. NFC can only be read at very close range just before contact, so it is limited to point-based location recording uses (such as passing checkpoints).

• Advantages: A major advantage is that it excels at bulk identification and inventory management. Because many tags can be read contactlessly and simultaneously, for example you can bulk-scan materials delivered to a site with RFID to register their locations. Radio waves can also penetrate obstacles, so materials can be detected even while still inside boxes. Depending on the scale of deployment, low running costs can also be attractive (passive RFID tags cost a few yen to a dozen-plus yen per tag).

• Disadvantages: It is not suitable for real-time location tracking. It cannot be used to continuously measure the coordinates of people or objects and is limited to point-by-point detection. Also note that there are initial costs to install tags and readers, and tag costs accumulate if many items are managed. Furthermore, depending on the frequency band, RFID can be vulnerable to metal and water, so consideration is needed for the tag target and environment.

Inertial sensors and PDR (Pedestrian Navigation)

Inertial Measurement Unit (IMU)-embedded accelerometers and gyroscopes are used to estimate the current position from distance traveled and heading; this method is called PDR (Pedestrian Dead Reckoning). Also known as pedestrian autonomous navigation, it is characterized by the ability to compute relative movement trajectories simply by a person carrying a smartphone or a dedicated device.

• Features: PDR is fundamentally a self-contained relative positioning method, and its advantage is that it does not rely on external radio signals or beacons. For example, when a worker carries a smartphone and moves, built-in sensors can detect steps and direction and estimate the approximate current position by accumulating movement vectors from the starting point. It is useful as a means to temporarily infer position during tunnel work or in enclosed spaces where radio signals do not reach.

• Accuracy: When used alone, PDR has the fatal problem that errors accumulate over time. Variations in stride length and sensor errors cause drift—moving more or less than actually traveled—to accumulate, and after several minutes to tens of minutes the positional error becomes non-negligible. Therefore, it is assumed that the system will be periodically reset/corrected using an external reference (an absolute position from another positioning system).

• Advantages: A benefit is that it can be used anywhere without being affected by the radio environment, and because it can be implemented using standard features of existing devices like smartphones, no special equipment is required. Even if its standalone accuracy is low, it can serve as a way to improve overall system stability by complementing positioning results from Wi‑Fi or beacons.

• Disadvantages: Due to the cumulative error problem, it is difficult to achieve long-duration, high-accuracy positioning with PDR alone. It also requires setting an absolute position at the start point, and if the starting point is incorrect, the entire subsequent trajectory will be offset. Because it requires periodic correction by other methods, it is rarely used alone in the field. It should be regarded primarily as an auxiliary means of position estimation.

Image recognition and marker-based positioning

In recent years, visual-based positioning that uses camera imagery and AR (augmented reality) technologies has also emerged. This method recognizes markers installed inside buildings (e.g., two-dimensional codes) or the shapes of surrounding structures with a camera to estimate one's position.

• Features: Using the camera of a smartphone, tablet, or AR glasses, location is determined by reading markers posted on walls or columns or by matching a pre-made indoor map with the currently visible scene. For example, scanning 2D codes placed at various points on a floor under construction identifies that location and recognizes it as “on floor X, in area Y.” Also, using SLAM (simultaneous localization and mapping) technology, it is becoming possible to track position with only a camera while moving, even without a prior map.

• Accuracy: In the camera-marker approach, accuracy depends on the marker placement intervals and the precision of image analysis. If markers are placed densely, the current area can be identified with errors of less than several tens of centimeters (less than several tens of inches), but if you move outside that range, positioning becomes impossible. With SLAM, errors of several meters (several ft) can accumulate, but because a map is being generated simultaneously, it has the advantage of continuing to estimate its own position even in enclosed spaces.

• Advantages: A key advantage is that no special radio equipment is required; it works with any camera-equipped device. As long as identifiable markers are posted, it does not depend on radio conditions and can provide high-precision location confirmation. Combined with AR technology, it can overlay navigation information and equipment installation positions directly on the camera feed at the site, contributing to DX (digital transformation) in construction management.

• Disadvantages: The challenges are the effort required and dependence on environmental conditions. With the marker method, markers must be placed beforehand at appropriate locations and densities, and if markers become peeled off or hidden as construction progresses, they become useless. Recognition rates also drop when the camera’s view is poor (dark conditions, high dust levels, etc.). In addition, SLAM has a high computational load and requires dedicated hardware or app development, so it is not something anyone can use immediately.

Points to consider when choosing indoor positioning technologies

As introduced above, even if you broadly speak of indoor location information systems, there is a wide variety of technologies. Each has its own strengths and limitations, so it is important to select the technology that fits the needs of the site. The main points to consider when introducing location information technologies indoors are summarized below.

• Required accuracy and real-time capability: First, clarify how much accuracy is needed on site. Do you need accuracy within several meters, or strict accuracy on the order of tens of centimeters to a few centimeters? The choice of technology differs accordingly. It is also important to determine whether you need to track people or objects in real time or whether point-position logging is sufficient. For example, BLE beacons are sufficient for basic material location tracking, but high-precision technologies such as UWB are required for accurate placement management of structures.

• Site environment (obstacles / area scale): Consider the construction site’s structure and scale. In environments with many steel frames, many rooms separated by walls, or underground floors, radio-based systems must account for signal attenuation and blind spots. Whether you want to cover a vast plant or an entire high-rise, or only a limited area, will change the appropriate technology and the number of devices required. For coarse coverage over wide areas, Wi‑Fi or long-range wireless communications can be considered; for precise measurement in localized areas, you would construct a UWB anchor network.

• Cost and schedule: Initial installation costs and operational costs are practical decision factors. Achieving high precision often requires high-cost equipment, so evaluate whether the investment is commensurate with the project scale. Also consider whether the system can be installed and calibrated within the construction schedule and whether deployment itself will interfere with site work. Simple beacons or tags can be deployed in a short period, whereas large-scale anchor installation requires preparation time.

• Operability and maintainability: Implementation is not the end; plan for ongoing operation and management. Battery-powered devices require regular battery replacement or charging, and devices may need to be added or relocated. Consider whether site staff can handle these tasks or whether specialist vendor support will be necessary. Simpler systems are easier to handle on site but may be inferior in accuracy and functionality. It is important to weigh the appropriate trade-offs.

• Integration with other systems and apps: How you will utilize collected location data is also a key point. Ideally, the system can integrate data with existing construction management software or safety management systems. Also confirm before implementation whether you can send notifications to site workers via smartphone apps or display real-time personnel deployment maps on managers’ PCs. Services that can output location data in common data formats or provide APIs increase extensibility later.

Taking all of the above into consideration, choosing an indoor positioning technology that suits the on-site requirements is the key to achieving the maximum effect cost-effectively. If necessary, combine multiple technologies; for example, "use UWB for precise positioning in primary areas and cover peripheral areas with BLE" or "normally track with beacons while occasionally measuring reference points with LRTK to verify accuracy" — consider hybrid deployments as well.

Recommendations for Simple Surveying with LRTK

We have compared indoor location information technologies, but in actual construction management, surveying work is indispensable for establishing high-precision reference points and for as-built (dekigata) management. In such situations, simple surveying using LRTK provided by our company is useful.

LRTK (pronounced 'L-R-T-K') is a solution developed to make it easy to deploy RTK (Real Time Kinematic), a high-precision GNSS positioning technology, on site. By combining a dedicated compact receiver and a communication service, it simplifies surveying tasks that were traditionally performed by specialist technicians using total stations and similar equipment into one-touch, few-centimeter accuracy position acquisition.

For example, if you use LRTK at points where satellite signals can be received—such as building rooftops or atriums—you can instantly obtain the precise coordinates of that location. Using those coordinates as a reference, you can carry out indoor positioning or use them to calibrate other indoor positioning systems. Because it uses network-based RTK correction information, there is no need to install a base station on site, and you can start using it anywhere nationwide as soon as a cellular signal is available.

By utilizing simplified surveying with LRTK, you can perform tasks such as establishing and surveying reference points at the start of construction, interim inspections, and final position checks quickly and with high accuracy. As a positioning information infrastructure that seamlessly connects indoor and outdoor environments, a major appeal is that it can provide a reliable positioning foundation even in environments where GPS cannot be used. For improved construction management efficiency and quality, please consider implementing LRTK solutions.

FAQ

Q: Why is location information important for indoor construction management? A: In indoor work, accurately knowing the locations of workers and materials enables rigorous safety management and improved work efficiency. In emergencies—such as rescuing personnel—or when required materials must be quickly located and transported, being able to instantly obtain location information enhances on-site responsiveness. Additionally, because construction progress can be managed spatially, it also aids process control and quality verification.

Q: Why can't GPS be used indoors? A: Because radio signals from GPS satellites have difficulty reaching indoors or underground and are blocked or attenuated by building structures. Even if a weak signal can be received, reflected signals from walls and columns can interfere and cause large errors (multipath), and the system cannot distinguish vertical differences (different floors), so practical accuracy cannot be obtained indoors.

Q: What types of indoor positioning systems are there? A: Methods that use Wi‑Fi signals, deploying Bluetooth beacons, high-precision positioning using UWB (ultra-wideband radio), area detection using RFID tags or NFC, image-recognition types using cameras and markers, and self-contained navigation using inertial sensors (PDR). Each differs in mechanism, accuracy, and required equipment, so it’s best to choose based on the characteristics explained in this article.

Q: What is the accuracy of indoor positioning technologies? A: It varies widely depending on the technology. Wi‑Fi and BLE beacons often have errors on the order of a few meters (a few ft). UWB is very high precision, ranging from several tens of centimeters (several tens of in) down to about 10 cm (3.9 in). RFID cannot provide continuous positioning but can determine whether something is within an area. Camera marker approaches depend on the density of marker placement, but if markers can be recognized they can pinpoint positions quite accurately. It is important to choose the technology according to the required accuracy.

Q: What methods are suitable if you want to manage indoor positioning while keeping costs down? A: If you want an easy start, positioning that leverages an existing Wi‑Fi network or systems using inexpensive BLE beacons are good candidates. These have relatively low initial deployment costs and work well for small areas or coarse location tracking. However, their accuracy and stability are inferior to more expensive systems, so assess whether they are sufficient for your use case. In some cases, it can be effective to deploy advanced technology only in areas that require high precision and complement the rest with low‑cost methods.

Q: What is LRTK? Can it be used indoors? A: LRTK is an RTK solution provided by our company that enables easy use of high-precision GNSS positioning. Although satellite signals cannot be received directly indoors, it can be applied to indoor surveying and alignment based on high-precision reference points obtained on rooftops or at openings in the building. By using LRTK, you can quickly set construction reference points and verify as-built conditions with an accuracy of a few centimeters, making it a highly reliable positioning foundation that supports indoor construction management.